1. Field of the Invention
This invention relates to an improvement in the process for resolving the reaction mixture that is formed in preparing propylene oxide and tertiary butyl alcohol by reacting propylene with tertiary butyl hydroperoxide in solution in tertiary butyl alcohol in the presence of a soluble molybdenum catalyst. More particularly, this invention is directed to substantially removing molybdenum from the reaction mixture.
Molybdenum compounds are somewhat toxic to livestock and, therefore, solutions containing molybdenum must be handled with care. Also, the presence of molybdenum in liquid by-products presents a disposal problem because of the limited toxicity of molybdenum to livestock.
The epoxidation reaction mixture that is formed when propylene is reacted with tertiary butyl hydroperoxide in solution in tertiary butyl alcohol in the presence of a soluble molybdenum epoxidation catalyst will normally comprise unreacted propylene, propylene oxide, tertiary butyl alcohol, unreacted tertiary butyl hydroperoxide, the soluble molybdenum catalyst and impurities, including C.sub.1 to C.sub.4 lower aliphatic carboxylic acids. The reaction mixture is usually separated by distillation into plurality of fractions including a recycle propylene fraction, a propylene oxide product fraction, a tertiary butyl alcohol product fraction and a heavy liquid distillation fraction containing tertiary butyl alcohol, unreacted tertiary butyl hydroperoxide and impurities, including substantially all of the dissolved molybdenum catalyst and a portion of the lower aliphatic carboxylic acid impurities.
In accordance with the present invention, the heavy liquid distillation fraction or a fraction thereof contain-ing from about 50 to 500 ppm of dissolved molybdenum is passed through a bed of a solid adsorbent consisting essen-tially of a synthetic, porous, high surface area amorphous magnesium silicate in order to substantially completely remove the dissolved molybdenum and to provide a liquid eluate containing not more than about 20 ppm of dissolved molybdenum.
The heavy liquid distillation fraction may initially contain as little as 0.03 wt. % (300 ppm) of dissolved molybdenum, but will normally contain from about 0.06 to about 0.6 wt. % (about 600 to about 6,000 ppm) of dissolved molybdenum. When the heavy liquid distillation fraction contains from about 300 to 500 ppm of dissolved molybdenum, it may be treated directly with the bed of synthetic, porous, high surface area amorphous magnesium silicate in order to substantially completely remove the dissolved molybdenum and to provide a liquid eluate containing not more than about 20 ppm of dissolved molybdenum. However, if the heavy liquid distillation fraction contains more than about 500 ppm of dissolved molybdenum, such as about 600 to about 6,000 ppm, as is usually the case, in accordance with a preferred embodiment of the present invention, the heavy liquid distillation fraction is first treated, non-catalytically, with a precipitating agent such as ammonia in a precipitation zone to form a precipitate comprising most of the dissolved molybdenum and from which a liquid fraction, such as a filtrate, can be recovered (e.g., by filtration) which will contain from about 50 to 500 ppm of dissolved molybdenum and which is charged, as feed, to the adsorption zone for treatment with the bed of synthetic, porous, high surface area amorphous magnesium silicate in order to substantially completely remove the dissolved molybdenum and to provide a liquid eluate containing not more than about 20 ppm of dissolved molybdenum.
The separate precipitate will comprise a concentrated solid molybdenum product that may be processed for the recovery of molybdenum. The precipitate will contain substantially all of the molybdenum present in the reaction mixture and, as a consequence, the thus-treated molybdenum fraction will pose a lesser environmental problem and can be disposed of more easily.
2. Prior Art
It is known to react propylene with tertiary butyl hy-droperoxide in the presence of a soluble molybdenum catalyst to provide a reaction product comprising propylene oxide and tertiary butyl alcohol. See, for example, Kollar U.S. Pat. No. 3,350,422, Kollar U.S. Pat. No. 3,351,635, and Russell U.S. Pat. No. 3,418,340.
It is also known to prepare soluble molybdenum catalysts to catalyze the reaction as disclosed, for example, in Bonetti et al. U.S. Pat. No. 3,480,563, Shum et al. U.S. Pat. No. 4,607,113, Marquis et al. U.S. Pat. No. 4,626,596, Marquis et al. U.S. Pat. No. 4,650,886, Marquis et al. U.S. Pat. No. 4,703,027, etc.
Kollar U.S. Pat. No. 3,860,662 is directed to an improvement in his basic process relating to the recovery of alcohols from the reaction product, which product is stated to be of an acidic nature, wherein a basic material such as an alkali metal or alkaline earth metal compound is added to the reaction mixture. Kollar U.S. Pat. No. 3,947,500 discloses a method for treating the reaction product formed by the reaction of an organic hydroperoxide with an olefin wherein an organic alcohol is formed as a by-product. It is stated that the alcohol tends to dehydrate and that to at least partially overcome this problem the oxidation reaction product is treated with an alkali metal or an alkaline earth metal compound. Kollar states that the alkali metal or alkaline earth metal compound can be added to the epoxidation reactor or to the reaction product.
Sorgenti U.S. Pat. No. 3,573,226 discloses a method wherein a molybdenum-containing catalyst solution is prepared by incorporating metallic molybdenum into the distillate bottoms fraction of an epoxidation reaction product followed by heating of the resultant mixture in order to form a soluble molybdenum-containing reaction product which can be used to catalyze the epoxidation reaction.
The molybdenum-catalyzed epoxidation of alpha olefins and alpha substituted olefins with hydroperoxides less stable than tertiary butyl hydroperoxide may be accomplished according to U.S. Pat. No. 3,862,961 to Sheng, et al. by employing a critical amount of a stabilizing agent consist-ing of a C.sub.3 to C.sub.9 secondary or tertiary monohydric alcohol, such as tertiary butyl alcohol. Citric acid is used to minimize the iron-catalyzed decomposition of the organic hydroperoxide without adversely affecting the reaction between the hydroperoxide and the olefin. A similar oxirane producing process is disclosed in Herzog in U.S. Pat. No. 3,928,393. The inventors in U.S. Pat. No. 4,217,287 discovered that if barium oxide is present in the reaction mixture, the catalytic epoxidation of olefins with organic hydroperoxides can be successfully carried out with good selectivity to the epoxide based on hydroperoxide converted when a relatively low olefin to hydroperoxide mole ratio is used. The alpha-olefinically unsaturated compound should be added incrementally to the organic hydroperoxide.
Maurin U.S. Pat. No. 3,931,044 is directed to a method for recovering molybdenum catalyst values from a peroxidation reaction product for recycle. Maurin discloses one of three techniques. In accordance with the first embodiment, the residue fraction is calcined to provide molybdenum trioxide which is then used to prepare a soluble molybdenum compound by reaction with aqueous ammonia. In a second embodiment, the molybdenum-containing fraction is treated with aqueous ammonia without calcining to form an ammonium molybdate which is treated with a polyalcohol to give a molybdic ester. In a third embodiment, the molybdenum-containing fraction is treated with gaseous ammonia in order to form an ammonium molybdate precipitate which can be recovered by filtration.
Harvey U.S. Pat. No. 3,449,217 is directed to a process for the recovery of tertiary butyl hydroperoxide from a mixture comprising tertiary butyl hydroperoxide, tertiary butyl alcohol and organic acids and esters result-ing from the liquid phase oxidation of isobutane by a pro-cess which minimizes hydroperoxide decomposition. This is done by accomplishing the distillation while the product has an effective pH of below about 9. The patentee teaches the treatment of the reactor effluent with a neutralizing agent such as an alkali metal or an alkaline earth metal hydroxide.
Levine U.S. Pat. No. 3,819,663 is directed to a method for treating a heavy distillation fraction of this nature in order to recover the molybdenum in the concentrated bottoms fraction for recycle to the epoxidation reaction zone as makeup catalyst.
Levine conducts his wiped-film evaporation process under conditions including a temperature of about 550-650.degree. F. (about 273.degree. to about 330.degree. C.) at atmospheric pressure to obtain his desired residual fraction for recycle as catalyst makeup and a distillate fraction comprising about 85% or more of the heavy distillation fraction. Levine states that the distillate fraction that is thus obtained can be used as a furnace fuel or can be worked up for recovery of the indi-vidual components contained therein. However, Levine et al. does not contain any teaching as to how the individual components in the fraction would be obtained.
U.S. Pat. No. 4,079,116 discloses a process for producing ammonium heptamolybdate from a molybdenum oxide concentrate involving, as one of the steps, the treatment of a filtrate with a cation exchange resin in order to recover molybdenum contained in the filtrate.
Su U.S. Pat. No. 4,328,191 discloses a process for recovering molybdenum from the catalyst residue derived from an olefin epoxidation process wherein the residue is treated with an oxidizing agent such as nitric acid, hydrogen peroxide, sodium hypochlorite, etc., to form an aqueous solution of molybdenum compounds that can be recovered by filtration. The aqueous filtrate contains organic residues that are removed by passing the filtrate through a bed of adsorbent, namely charcoal, to remove the organic residues. Thereafter, molybdenum is recovered from the thus-treated filtrate.
In Canavesi U.S. Pat. No. 4,331,567, a process is disclosed that is directed to the preparation of an olefin epoxidation catalyst containing both ferric and molybdenum salts, a processing step is employed wherein a filtrate formed during a filtration step is treated with an anionic exchange resin in order to recover molybdenum contained in the filtrate.
Canavasi U.S. Pat. No. 4,401,631 discloses a process for recovering molybdenum from catalyst residues from an olefin epoxidation process wherein the spent catalyst, in the oxide form, is treated with an aqueous alkali metal hydroxide to solubilize the molybdenum in the form of an alkali metal molybdate and is then treated with a strong cationic exchange resin to convert the molybdate to molybdic acid.
A process for recovering the molybdenum contained in an olefin epoxidation catalyst is disclosed in Moore et al. U.S. Pat. No. 4,405,572 wherein a catalyst-containing residue fraction is treated with an aqueous alkaline material to form a molybdenum-containing aqueous phase from which the molybdenum can be recovered by acidification and precipitation or by treatment with a cation exchange resin.